power torque calculator

What This Power Torque Calculator Does

This tool solves the core rotating-machine relationship between power, torque, and speed (RPM). You can calculate any one of these three values when the other two are known.

• Calculate power from torque and RPM
• Calculate torque from power and RPM
• Calculate RPM from power and torque
• Work in practical units: kW, hp, W, N·m, and lb-ft

The Core Relationship: Power, Torque, and RPM

For rotating systems, mechanical power is torque multiplied by angular speed:

From this equation, you can rearrange:

• T (N·m) = P (W) × 60 / (2π × RPM)
• RPM = P (W) × 60 / (2π × T (N·m))

Handy Shortcut Forms

• kW = N·m × RPM / 9549 (approx.)
• hp = lb-ft × RPM / 5252 (for imperial units)

How to Use This Calculator

1) Choose what to calculate

Select Power, Torque, or RPM in the dropdown.

2) Enter the two known values

The field being calculated becomes read-only. Enter only the two known inputs and choose your units.

3) Click Calculate

You will get the result in your selected unit, plus equivalent conversions for quick comparison.

Worked Examples

Example 1: Calculate Power

Suppose a motor delivers 200 N·m at 3000 RPM. Power = 200 × 2π × 3000 / 60 ≈ 62,832 W = 62.83 kW (about 84.25 hp).

Example 2: Calculate Torque

If an engine produces 150 hp at 4000 RPM, first convert 150 hp to watts, then solve for torque. The result is roughly 267 N·m (about 197 lb-ft).

Example 3: Calculate RPM

If you need 10 kW from a shaft delivering 25 N·m, then RPM = 10,000 × 60 / (2π × 25) ≈ 3819.7 RPM.

Why Unit Consistency Matters

Most calculation errors happen because units are mixed incorrectly. This calculator handles conversions automatically, but understanding the base SI relationship helps you validate results:

• Power base unit: Watt (W)
• Torque base unit: Newton-meter (N·m)
• Speed base unit used in tool input: RPM

Quick Conversion Reference

Common Mistakes to Avoid

• Using RPM as rad/s without conversion
• Mixing hp with N·m directly in SI formulas
• Forgetting that calculated values should be positive and realistic
• Comparing crankshaft power and wheel power as if they were the same measurement point

Where This Is Useful

• Automotive tuning and dyno analysis
• Electric motor sizing for machines and robotics
• Pump/fan drive calculations
• Gearbox selection and shaft design checks

FAQ

Is higher torque always better?

Not by itself. Performance depends on both torque and RPM because power combines both.

Why does the number 5252 appear in horsepower calculations?

In imperial units, hp and lb-ft with RPM simplify to hp = (lb-ft × RPM) / 5252. It comes from unit definitions and conversion constants.

Can I use this for electric motors and combustion engines?

Yes. The physics is the same for any rotating shaft as long as inputs are accurate.